Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for a variable displacement compressor, which can be realized with a simple construction, while being equipped with the function of a check valve to be disposed at an outlet port of the compressor. The control valve for a variable displacement compressor includes a main valve that sets a cross-sectional area-fixed passage in which the passage cross-sectional area thereof is substantially constant when refrigerant flows between a discharge chamber and an outlet port of the compressor, and closes the cross-sectional area-fixed passage due to inversion of the magnitudes of pressure across the cross-sectional area-fixed passage when the compressor is not in operation, a pilot valve that controls the flow rate of refrigerant flowing from the discharge chamber to a crankcase in a manner interlocked with the differential pressure across the cross-sectional area-fixed passage received by the main valve, and a solenoid that is capable of setting a valve lift of the pilot valve by an external signal. The pilot valve controls the flow rate of refrigerant allowed to flow into the crankcase so as to make constant the differential pressure across the cross-sectional area-fixed passage, to thereby provide control such that the flow rate of refrigerant allowed to flow to the outlet port of the compressor is constant.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY

This application claims priority of Japanese Application No. 2004-174154 filed on Jun. 11, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor, which is mounted in the compressor and capable of providing control such that a flow rate of refrigerant discharged therefrom becomes constant.

(2) Description of the Related Art

A compressor used in a refrigeration cycle of an automotive air conditioner, for compressing refrigerant, uses an engine as a drive source, and hence is incapable of performing rotational speed control. To eliminate the inconvenience, a variable displacement compressor capable of varying refrigerant capacity (the discharge amount of refrigerant) is employed so as to obtain an adequate cooling capacity without being constrained by the rotational speed of the engine.

In such a variable displacement compressor, a wobble plate (swash plate) fitted on a shaft driven by the engine for rotation has pistons connected thereto, and is rotated within a crankcase while varying the inclination angle thereof, whereby the stroke of the pistons is varied to vary the capacity of the compressor, i.e. the discharge amount of refrigerant.

To change the inclination angle of the wobble plate, part of compressed refrigerant is introduced into the hermetically closed crankcase to cause a change in the pressure in the crankcase, whereby the balance of pressures acting on the opposite sides of each piston connected to the wobble plate is changed to continuously change the inclination angle of the wobble plate.

The pressure in the crankcase is changed by a control valve for a variable displacement compressor, which is disposed in a refrigerant passage extending between the refrigerant discharge chamber and the crankcase or a refrigerant passage extending between the crankcase and the suction chamber. This control valve provides control such that the communication through the refrigerant passages is allowed or blocked so as to maintain the differential pressure thereacross at a predetermined value, and more particularly, the differential pressure can be set to the predetermined value by externally changing a value of control current supplied to the control valve. With this configuration, when the rotational speed of the engine rises, the pressure introduced into the crankcase is increased to reduce the volume of refrigerant that can be compressed, whereas when the rotational speed of the engine lowers, the pressure introduced into the crankcase is reduced to increase the volume of refrigerant that can be compressed, whereby the amount of refrigerant discharged from the compressor is maintained constant.

One known method of controlling the capacity of such a variable displacement compressor uses a control valve therefor, which provides control such that the flow rate of refrigerant discharged from the compressor becomes constant (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2004-116349).

This control valve for a variable displacement compressor, which provides control such that the flow rate of refrigerant flowing through the compressor becomes constant, includes a cross-sectional area variable passage which is capable of changing the passage area of a refrigerant passage through which flows the refrigerant discharged from the compressor, using a solenoid by an external signal supplied thereto, and controls the flow rate of refrigerant introduced from the discharge chamber into the crankcase such that the differential pressure across the cross-sectional area variable passage becomes equal to a predetermined value. By holding the differential pressure across the cross-sectional area variable passage set to a certain passage cross-sectional area, at the predetermined value, the flow rate of refrigerant passing through the variable orifice is controlled to be constant.

However, the conventional control valve for a variable displacement compressor is configured such that it includes a first control valve that varies the passage cross-sectional area of the refrigerant passage, a solenoid section that sets the passage cross-sectional area according to changes in external conditions, and a second control valve that senses the differential pressure occurring across the first control valve and controls the pressure in the crankcase such that the differential pressure becomes equal to the predetermined value, and the first control valve through which high-pressure refrigerant is allowed to pass is controlled by the solenoid section to thereby directly change the passage cross-sectional area. Therefore, this control valve suffers from the problems that it is not easy to change the large passage cross-sectional area by the solenoid section, and the overall construction of the control valve is complicated.

Further, in the variable displacement compressor, there occurs a large differential pressure between during operation and during stoppage of operation, and when the compressor is changed from an operating state into a non-operating state, pressure corresponding to the differential pressure is returned to the discharge chamber instantaneously. Therefore, when the operation is resumed, the compressor starts compression of refrigerant from its state without the differential pressure, which degrades operating efficiency. To prevent refrigerant discharged from the compressor from returning during stoppage of operation, a check valve is disposed on the outlet port of the compressor. This has been a factor increasing the cost of the compressor.

SUMMARY OF THE INVENTION

The present invention has been made in view of these problems, and an object thereof is to provide a control valve for a variable displacement compressor, which can be realized with a simple construction, while being equipped with the function of a check valve to be disposed at an outlet port of the compressor.

To solve the above problem, the present invention provides a control valve for a variable displacement compressor, for providing control such that a flow rate of refrigerant discharged from the compressor becomes constant, comprising a main valve that is disposed in a first refrigerant passage formed between a first port communicating with a discharge chamber of the compressor and a second port communicating with an outlet port of the compressor, such that the main valve is lifted in a valve-opening direction to set the first refrigerant passage to a cross-sectional area-fixed passage having a predetermined passage cross-sectional area in response to a flow of refrigerant from the first port to the second port, and closed when a flow rate of the flow of refrigerant is slight or zero, a pilot valve that is disposed into a second refrigerant passage formed between the first port and a third port communicating with a crankcase of the compressor, for controlling a flow rate of refrigerant flowing from the first port to the third port according to a differential pressure across the cross-sectional area-fixed passage, and a solenoid that sets the pilot valve to a predetermined valve lift by an external signal.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conceptual configuration of a variable displacement compressor.

FIG. 2 is a cross-sectional view showing details of a control valve for a variable displacement compressor, according to a first embodiment of the present invention, in a state during deenergization.

FIG. 3 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is controlled to its maximum capacity.

FIG. 4 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is subjected to variable displacement control.

FIG. 5 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is controlled to its minimum capacity.

FIG. 6 is a cross-sectional view showing details of a control valve according to a second embodiment, in a state during deenergization.

FIG. 7 is a cross-sectional view showing details of a control valve according to a third embodiment, in a state during deenergization.

FIG. 8 is a cross-sectional view showing a control valve according to a fourth embodiment, in a state where the compressor is subjected to variable displacement control.

FIG. 9 is a cross-sectional view showing a control valve according to a fifth embodiment, in a state where the compressor is subjected to variable displacement control.

FIG. 10 is a cross-sectional view showing a control valve according to a sixth embodiment, in a state where the compressor is subjected to variable displacement control.

FIG. 11 is a cross-sectional view showing a control valve according to a seventh embodiment, in a state where the compressor is subjected to variable displacement control.

FIG. 12 is an expanded cross-sectional view showing a main valve element used in a main valve of the control valve for a variable displacement compressor, according to the seventh embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of the present invention will be described in detail with reference to the drawings showing control valves applied to a variable displacement compressor for a clutchless type in which the variable displacement compressor is directly connected to an engine for an automotive vehicle, and for a fixed flow rate control type in which the flow rate of discharged refrigerant is controlled to be constant, by way of example.

FIG. 1 is a cross-sectional view of a conceptual configuration of a variable displacement compressor.

The variable displacement compressor includes a hermetically formed crankcase 1, which contains a rotating shaft 2 rotatably supported therein. One end of the rotating shaft 2 extends via a shaft seal device, not shown, to the outside of the crankcase 1, and a pulley 3 transmitted a drive force from an engine for an automotive vehicle is fixed to the one end of the rotating shaft 2. The rotating shaft 2 has a wobble plate 4 fitted thereon such that the inclination angle of the wobble plate 4 can be varied. Around the axis of the rotating shaft 2, there are arranged a plurality of cylinders 5 (one of which is shown in FIG. 1). Each cylinder 5 has a piston 6 disposed therein, for converting the rotating and wobbling motion of the wobble plate 4 into reciprocating motion. The cylinder 5 is connected to a suction chamber 9 and a discharge chamber 10 via a suction relief valve 7 and a discharge relief valve 8. A control valve 11 for a variable displacement compressor is provided between the discharge chamber 10 and an outlet port formed to communicate therewith and between the discharge chamber 10 and the crankcase 1, and an orifice 12 is provided between the crankcase 1 and the suction chamber 9.

In the variable displacement compressor, the outlet port formed to communicate with the discharge chamber 10 is connected via a high-pressure refrigerant conduit line to a condenser 13, from which piping extends to an inlet port formed to communicate with the suction chamber 9 via an expansion valve 14, an evaporator 15, and a low-pressure refrigerant conduit line, whereby a refrigeration cycle as a closed circuit is formed.

In the variable displacement compressor constructed as above, as the rotating shaft 2 to which the drive force is transmitted from the engine is rotated, the wobble plate 4 fitted on the rotating shaft 2 wobbles while rotating. This causes each piston 6 connected to the outer peripheral part of the wobble plate 4 to perform reciprocating motion in a direction parallel to the axis of the rotating shaft 2, whereby refrigerant at suction pressure Ps in the suction chamber 9 is drawn into the associated cylinder 5 and compressed therein, and the compressed refrigerant at discharge: pressure Pd1 is discharged into the discharge chamber 10. At this time, high-pressure refrigerant in the discharge chamber 10 is decompressed to discharge pressure Pd2 when passing through the control valve 11, and delivered from the outlet port to the condenser 13. Part of the high-pressure refrigerant is introduced into the crankcase 1 via the control valve 11. This causes the pressure Pc in the crankcase 1 to rise, whereby the inclination angle of the wobble plate 4 is set such that the bottom dead center of the piston 6 is brought to a position where the pressure in the cylinder 5 and the pressure Pc in the crankcase 1 are balanced. Thereafter, the refrigerant introduced into the crankcase 1 is returned to the suction chamber 9 via the orifice 12.

The control valve 11 detects the differential pressure (Pd1-Pd2) which is generated across a refrigerant passage having a predetermined cross-sectional area set thereto when refrigerant delivered from the discharge chamber 10 passes through the refrigerant passage, and introduces the refrigerant into the crankcase 1 at a flow rate dependent on the detected differential pressure, thereby providing control such that the flow rate of the refrigerant sent from the discharge chamber 10 to the condenser 13 becomes constant. More specifically, as the rotational speed of the engine increases, the suction pressure Ps lowers, and the discharge pressure Pd1 rises. When this increases the flow rate of refrigerant sent from the discharge chamber 10 to the condenser 13 via the control valve 11, thereby increasing the differential pressure (Pd1-Pd2) across the control valve, the flow rate of refrigerant introduced into the crankcase 1 also increases, whereby the pressure Pc in the crankcase 1 increases. Accordingly, in the variable displacement compressor, the wobble plate 4 is inclined in such a direction as will cause the wobble plate 4 to become at right angles to the rotating shaft 2 to decrease the stroke of the pistons 6, which acts on the compression capacity of the cylinders 5 in a reducing direction to reduce the discharge flow rate of refrigerant. Thus, even when the flow rate of discharged refrigerant is about to increase due to an increase in the rotational speed of the engine, the control valve 11 increases the flow rate of refrigerant introduced into the crankcase 1 according to the increase in the flow rate of refrigerant, whereby the pressure Pc in the crankcase 1 is increased to reduce the discharge capacity. Therefore, the flow rate of refrigerant discharged from the compressor is controlled to be constant.

Inversely, when the rotational speed of the engine lowers, the flow rate of refrigerant sent from the discharge chamber 10 to the condenser 13 via the control valve 11 decreases to decrease the differential pressure (Pd1-Pd2) across the control valve 11, whereby the flow rate of refrigerant introduced into the crankcase 1 also decreases to lower the pressure Pc in the crankcase 1. As a result, the discharge flow rate of refrigerant is increased whereby the flow rate of discharged refrigerant is controlled to be constant.

Next, a description will be given of examples of the construction of the control valve for a variable displacement compressor.

FIG. 2 is a cross-sectional view showing details of a control valve for a variable displacement compressor, according to a first embodiment of the present invention, in a state during deenergization.

The control valve 11 has a main valve 20, a pilot valve 21, and a solenoid 22, and is accommodated in a body 23 in a manner such that the main valve 20, the pilot valve 21, and the solenoid 22 are arranged on the same axis. The body 23 is provided with three ports 24, 25 and 26 which form refrigerant outlets and an inlet of the main valve 20 and the pilot valve 21. When the control valve 11 is mounted in the variable displacement compressor, the port 24 communicates with the discharge chamber 10 for introduction of refrigerant at discharge pressure Pd1. The port 25 communicates with the outlet port of the compressor for delivery of refrigerant at discharge pressure Pd2. The port 26 communicates with the crankcase 1 of the compressor for delivery of refrigerant at the controlled pressure Pc.

The body 23 has a refrigerant passage 27 formed therein to communicate between the port 24 and the port 25 One end of the refrigerant passage 27 toward the port 25 forms a main valve seat 28 of the main valve 20, using the refrigerant passage 27 as a valve hole of the main valve seat 28. On the downstream side of the valve seat 28, a main valve element 29 is disposed in a manner opposed to the main valve seat 28 such that the main valve element 29 is movable to and away from the main valve seat 28. Disposed in a space communicating with the port 25 is a spring 30 having a weak spring force for urging the main valve element 29 in a valve-closing direction, whereby the main valve 20 is configured to have a check valve structure.

Furthers, the body 23 has a refrigerant passage 31 formed therein to communicate between the port 24 and the port 26. One end of the refrigerant passage 31 toward the port 24 forms a valve seat 32 of the pilot valve 21, using the refrigerant passage 31 as a valve hole of the valve seat 32. On the upstream side of the valve seat 32, a valve element 33 is disposed in a manner opposed to the valve seat 32 such that the valve element 33 is movable to and away from the valve seat 32, thereby forming a poppet valve. A spring 34 is disposed in a space communicating with the port 24, for urging the valve element 33 in a valve-opening direction.

The valve element 33 has a hollow cylindrical shape, and is integrally formed with a drive shaft 35 of the solenoid 22. The drive shaft 35 is disposed in a manner extending through a through hole axially formed in the main valve element 29 of the main valve 20, whereby the main valve element 29 of the main valve 20 is axially movably held on the drive shaft 35. Further, the drive shaft 35 has a stop ring 36 fitted thereon as a stopper member. When the main valve element 29 of the main valve 20 is lifted in a direction away from the main vale seat 28, the main valve element 29 is stopped by the stop ring 36 so as to set the main valve 20 to a cross-sectional area-fixed passage having a predetermined cross-sectional area. The stop ring 36 is disposed at an approximately intermediate position in the range of the stroke of the drive shaft 35 to be exhibited when the pilot valve 21 is within a control range. The location of the stop ring 36 is set such that the main valve element 29 is stopped by the stop ring 36 at such a lift position that the main valve 20 has the predetermined cross-sectional area. As a result, when the control valve 11 is performing control, in the main valve 20, the passage cross-sectional area defined by a gap between the main vale seat 28 and the main valve element 29 is held approximately constant. This is because when the pilot valve 21 is performing a control operation, a change in the passage cross-sectional area of the main valve 20 with respect to the stroke of the valve element 33 is very small, so that it is possible to consider that the passage cross-sectional area of the main valve 20 is substantially constant. Thus, when refrigerant is flowing through the main valve 20, the main valve element 29 of the main valve 20 is stopped by the stop ring 36 such that the main valve element 29 moves in unison with the valve element 33 of the pilot valve 21. Therefore, a change in the flow rate of refrigerant flowing through the main valve 20 having a passage cross-sectional area set to be substantially constant causes a change in the differential pressure across the main vale 20, and the main valve element 29 of the main valve 20 senses the change in the differential pressure to axially displace itself. The displacement of the main valve element 29 sets the axial displacement of the valve element 33 of the pilot valve 21.

The solenoid 22 has a bottomed sleeve 37 having an open end thereof hermetically fixed to the body 23, and a core 38 is fitted in the opening of the bottomed sleeve 37. The core 38 has a through hole formed therethrough along the axis thereof, and axially movably holds the drive shaft 35. A plunger 39 is disposed within the bottomed sleeve 37 in a manner movable to and away from the core 38. Fitted in the plunger 39 is an upper end of the drive shaft 35, as viewed in FIG. 2, which is held by the core 38, and the plunger 39 is urged by the spring 34 of the pilot valve 21 via the drive shaft 35 in a direction away from the core 38. A coil 40 is circumferentially provided outside the bottomed sleeve 37, and surrounded by a yoke 41 integrally formed with the body 23. The yoke 41 has an annular plate 42 fitted in an upper end thereof, as viewed in. FIG. 2, between the yoke 41 and the plunger 39, for forming a magnetic circuit.

Further, the drive shaft 35 which has a hollow structure, and the upper end thereof, as viewed in FIG. 2, fitted in the plunger 39, has a hole 43 formed in a lateral side thereof such that the inside of the bottomed sleeve 37 closed by the core 38 and the refrigerant passage 31 on the downstream side of the pilot valve 21 communicate with each other. This causes the pressure Pc to equally act on the axially opposite ends of the valve element 33 and the drive shaft 35, respectively, thereby enabling the solenoid 22 to control the pilot valve 21 without being adversely affected by the pressure Pc.

In the control valve 11 constructed as above, when the solenoid 22 is in a deenergized state in which no control current is supplied to the solenoid 22 by an external signal supplied thereto, in other words, when the automotive air conditioner is in a non-operating state, the main valve 20 is fully closed by having the main valve element 29 seated on the main valve seat 28 by the urging force of the spring 30, and the pilot valve 21 is fully open since the valve element 33 is urged by the spring 34 in the valve-opening direction. Therefore, all the refrigerant discharged from the compressor driven by the engine is always introduced into the crankcase 1 via the pilot valve 21, which places the compressor in the minimum capacity operating state. In the minimum capacity operation, the flow rate of refrigerant discharged from the compressor is very small, so that the discharge pressure Pd1 is small and not large enough to push open the main valve element 29 of the main valve 20 against the urging force of the spring 30.

Further, the FIG. 2 showing the state of the control valve 11 during deenergization also shows a state of the automotive air conditioner immediately after the air conditioner is changed from an operating state into the non-operating state. More specifically, when the automotive air conditioner is in operation, and the solenoid 22 is energized, the plunger 39 of the solenoid 22 is attracted to the core 38, whereby the drive shaft 35 is pushed downward, as viewed in the figure, to place the pilot valve 21 in the fully closed state or in a state where the valve lift thereof is controlled. Therefore, the compressor is operating in a variable displacement region, and hence refrigerant at discharge pressure Pd1, delivered from the discharge chamber 10, is introduced into the port 24 of the control valve 11. At this time, in the main valve 20, the main valve element 29 is lifted from the main valve seat 28 by the discharge pressure Pd1, and refrigerant decompressed to discharge pressure Pd2 is delivered from the port 25. In this state, when the automotive air conditioner stops its operation, the discharge pressure Pd1 sharply decreases to invert the relationship between the discharge pressure Pd1 at the port 24 and the discharge pressure Pd2 at the port 25, and the refrigerant at discharge pressure Pd2, having been sent from the port 25, is about to flow upstream, but, as shown in FIG. 2, the main valve 20 is fully closed by the discharge pressure Pd2, thereby enabling the refrigerant at the port 25 to maintain the high discharge pressure Pd2. Therefore, when the automotive air conditioner is started again, a rise time required until the discharge pressure Pd1 recovers to the maintained high discharge pressure Pd2 is shortened.

Next, a description will be given of the operation of the control valve 11 in the state where the compressor is in the variable displacement region.

FIG. 3 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is controlled to its maximum capacity. FIG. 4 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is subjected to variable displacement control. FIG. 5 is a cross-sectional view showing the control valve according to the first embodiment, in a state where the compressor is controlled to its minimum capacity.

When the automotive air conditioner starts its operation, the control valve 11 controls the compressor to its maximum capacity. That is, control current corresponding to the maximum capacity is supplied to the solenoid 22. As a result, the plunger 39 is attracted to the core 38, and moved downward, as viewed in FIG. 3, to thereby seat the valve element 33 integrally formed with the drive shaft 35 on the valve seat 32 to fully close the pilot valve 21.

This causes the flow rate of refrigerant introduced into the crankcase 1 to be reduced to zero, whereby the compressor starts its maximum capacity operation. Refrigerant at discharge pressure Pd1, delivered from the discharge chamber 10, is introduced into the port 24, lifts the main valve element 29 of the main valve 20 from the main valve seat 28, passes through a gap (passage having a constant cross-sectional area) between the main valve element 29 and the main valve seat 28 produced by the lift of the main valve element 29, and is delivered from the port 25 while being decompressed to discharge pressure Pd2. At this time, the main valve element 29 of the main valve 20 is stopped by the stop ring 36 fitted on the drive shaft 35, and the passage cross-sectional area formed by the gap between the main valve element 29 and the main valve seat 28 is fixed.

When cooling load on the automotive air conditioner decreases, control current dependent on the cooling load is supplied to the solenoid 22 of the control valve 11. This causes the plunger 39 to be moved by the urging force of the spring 34 in the direction away from the core 38, and in accordance with the movement of the plunger 39, the pilot valve 21 is set to a valve lift dependent on the control current, as shown in FIG. 4. The pilot valve 21 decompresses refrigerant introduced into the port 24 at discharge pressure Pd1, to the pressure Pc, and supplies the refrigerant from the port 26 to the crankcase 1 at a flow rate dependent on the valve lift.

Now, when the discharge capacity of the compressor is increased e.g. due to an increase in the rotational speed of the engine, the discharge pressure Pd1 increases to increase the differential pressure (Pd1-Pd2) across the main valve 20, whereby a force to push open the main valve element 29 of the main valve 20 is increased and about to further lift the main valve element 29. When the main valve element 29 is lifted, the valve element 33 of the pilot valve 21, formed integrally with the drive shaft 35 stopping the main valve 29 is also lifted in a manner interlocked with the lift of the main valve element 29. This increases the flow rate of refrigerant supplied to the crankcase 1, so that the compressor operates in a direction of reducing the discharge capacity thereof to lower the discharge pressure Pd1 to thereby restore the differential pressure across the main valve 20 to its original state. Inversely, when the discharge capacity of the compressor decreases e.g. due to a decrease in the rotational speed of the engine, the compressor operates in a direction of increasing the discharge capacity thereof to restore the differential pressure across the main valve 20 to its original state. As a result, the control valve 11 operates to provide control such that refrigerant is discharged from the compressor at a constant flow rate.

When the cooling load on the automotive air conditioner becomes sufficiently low, the control current dependent on the sufficiently low cooling load is supplied to the solenoid 22 of the control valve 11. As shown in FIG. 5, this causes the solenoid 22 to set the valve lift of the pilot valve 21 to the maximum or its vicinity, to thereby set the flow rate of refrigerant supplied from the port 26 to the crankcase 1 to the maximum or its vicinity. As a result, the compressor is controlled to the minimum discharge capacity or its vicinity.

FIG. 6 is a cross-sectional view showing details of a control valve for a variable displacement compressor, according to a second embodiment of the present invention, in a state during deenergization. It should be noted that component elements in FIG. 6 identical to those shown in FIGS. 2 to 5 are designated by identical reference numerals, and detailed description thereof is omitted.

The control valve 51 according to the second embodiment is distinguished from the control valve 11 according to the first embodiment in that the structure of the drive shaft 35 of the solenoid 22 is modified. More specifically, in the control valve 51, the solenoid 22 has a first drive shaft 52 having one end thereof fitted in the plunger 39, and the other end thereof slidably held by a cylinder formed in the core 38. The core 38 also holds a hollow cylindrical second drive shaft 53 integrally formed with the valve element 33 of the pilot valve 21, in a manner movable axially back and forth. The solenoid 22, the main valve 20, and the pilot valve 21 are capable of performing their predetermined functions only provided that they are arranged on the same axis. However, by dividing a drive portion of the solenoid 22 into the first drive shaft 52 and the second drive shaft 53, as described above, the solenoid 22 can at least tolerate misalignment of the main valve 20 and the pilot valve 21 from the axis, to some extent.

The second drive shaft 53 has a groove 54 formed in an outer periphery of a part thereof, which is held by the core 38. The groove 54 has a function of preventing high-pressure refrigerant at discharge pressure Pd2 from leaking through a clearance between the second drive shaft 53 and the core 38 into the inside of the bottomed sleeve 37, in which pressure is made equal to the pressure Pc at the port 26 via the hollow part of the second drive shaft 53.

Further, the second drive shaft 53 holds the main valve element 29 of the main valve 20 in a manner movable axially back and forth. Therefore, when the relationship between the discharge pressure Pd1 and the discharge pressure Pd2 which was lower than the discharge pressure Pd1 is inverted, as in the case of immediately after the automotive air conditioner has stopped its operation, and the main valve 20 is functioning as a check valve, refrigerant at pressure Pd2 sometimes leaks from a clearance between the second drive shaft 53 and the main valve element 29, and flows upstream. To eliminate this inconvenience, the second drive shaft 53 has a protrusion 55 integrally formed therewith such that it extends radially outward and a face thereof opposed to the main valve element 29 has a tapered shape. The protrusion 55 is configured such that it can also be used as a stopper for receiving the spring 34 urging the second drive shaft 53 toward the first drive shaft 52. Therefore, when the main valve element 29 is seated on the main valve seat 28 by the discharge pressure Pd2 to close the main valve 20, since the second drive shaft 53 is urged upward, as viewed in FIG. 6, by the spring 34, the protrusion 55 functions as a stop valve which is brought into abutment with the main valve element 29 for closing the clearance between the second drive shaft 53 and the main valve element 29.

FIG. 7 is a cross-sectional view showing details of a control valve for a variable displacement compressor, according to a third embodiment of the present invention, in a state during deenergization. It should be noted that component elements in FIG. 7 identical to those shown in FIG. 6 are designated by identical reference numerals, and detailed description thereof is omitted.

The control valve 61 according to the third embodiment is distinguished from the control valve 51 according to the second embodiment in that operations of the main valve 20 and the pilot valve 21, including the second drive shaft 53, are made more stables. More specifically, in the control valve 61, guides 62 are integrally formed with the valve element 33 of the pilot valve 21 in a manner axially extended from the valve element 33. The guides 62 provided three in total are arranged around a pressure-equalizing hole formed through the foremost end of the valve element 33 such that an outer peripheral portion of each guide 62 is in sliding contact with the inner wall of a valve hole of the pilot valve 21. As a result, the second drive shaft 53 has one end thereof held by the core 38, and the other end thereof held by the valve hole of the pilot valve 21, which enables the main valve element 29 of the main valve 20 and the valve element 33 of the pilot valve 21 to operate while maintaining the coaxial status, even if lateral load is applied thereto by the flow of high-pressure refrigerant.

FIG. 8 is a cross-sectional view showing a control valve for a variable displacement compressor, according to a fourth embodiment of the present invention, in a state where the compressor is subjected to variable displacement control. It should be noted that component elements in FIG. 8 identical to those shown in FIGS. 2 to 5 are designated by identical reference numerals, and detailed description thereof is omitted.

The control valve 71 according to the fourth embodiment is distinguished from the control valve 11 according to the first embodiment in that the structure of the pilot valve 21 is modified. More specifically, in the control valve 71, the drive shaft 35 and the valve element 33 of the pilot valve 21 are formed by a pipe having a straight shape, and the outer diameter of the pipe is formed to be close to the inner diameter of the valve hole of the pilot valve 21 such that the valve element 33 can be inserted in and removed from the valve hole of the pilot valve 21. This enables the pilot valve 21 to function as a slide valve. When the compressor is controlled to the maximum capacity, as in the case of the automotive air conditioner having been started, the pilot valve 21 is fully closed by having the valve element 33 inserted into its valve hole. Further, when the compressor is subjected to variable displacement control, the pilot valve 21 is set to a predetermined valve lift by having the valve element 33 removed from its valve hole.

FIG. 9 is a cross-sectional view showing a control valve for a variable displacement compressor, according to a fifth embodiment of the present invention, in a state where the compressor is subjected to variable displacement control. It should be noted that component elements in FIG. 9 identical to those shown in FIGS. 2 to 5 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 11 according to the first embodiment in which when the valve lift of the pilot valve 21 is controlled by the solenoid 22, the valve lift of the main valve 20 is more or less changed to slightly change the passage cross-sectional area of the main valve 20, in the control valve 81 according to the fifth embodiment, the passage cross-sectional area of the main valve 20 is completely fixed to be constant. More specifically, in the control valve 81, the main valve element 29 of the main valve 20 has a concentrically shaped extended portion 82 which is integrally formed therewith such that the extended portion 82 is always partially positioned in the valve hole, whereby between the outer peripheral surface of the extended portion 82 of the main valve element 29 and the inner peripheral surface of the valve hole, there is formed a passage which has a cross-sectional area unchangeable with respect to a change in the stroke of the main valve element 29 along the axis thereof. Therefore, during variable displacement control of the compressor, the main valve 20 functions as a cross-sectional area-fixed passage which is unchangeable in cross-sectional area, and when the magnitude of pressure of refrigerant is inverted across the main valve 20 as in the case of immediately after the automotive air conditioner has stopped its operation, the main valve 20 functions as a check valve.

FIG. 10 is a cross-sectional view showing a control valve for a variable displacement compressor, according to a sixth embodiment of the present invention, in a state where the compressor is subjected to variable displacement control. It should be noted that component elements in FIG. 10 identical to those shown in FIG. 9 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 81 according to the fifth embodiment in which the cross-sectional area-fixed passage of the main valve 20 is formed on the upstream side of the main valve seat 28, in the control valve 91 according to the sixth embodiment, the cross-sectional area-fixed passage of the main valve 20 is formed on the downstream side of the main valve seat 28. More specifically, in the control valve 91, the main valve element 29 of the main valve 20 is formed to have an axially long shape, and is configured such that a passage having a predetermined cross-sectional area is formed between the outer peripheral surface of the main valve element 29 and the inner peripheral surface of a cylinder containing the same. As a result, in the main valve 20, refrigerant having passed through a gap between the main valve element 29 and the main valve seat 28 passes through the cross-sectional area-fixed passage having a predetermined cross-sectional area.

FIG. 11 is a cross-sectional view showing a control valve for a variable displacement compressor, according to a seventh embodiment of the present invention, in a state where the compressor is subjected to variable displacement control. FIG. 12 is a fragmentary expanded cross-sectional view of a main valve element used in a main valve of the control valve according to the seventh embodiment. It should be noted that component elements in FIG. 11 identical to those shown in FIG. 9 are designated by identical reference numerals, and detailed description thereof is omitted.

As is distinct from the control valve 81 according to the fifth embodiment in which the cross-sectional area-fixed passage of the main valve 20 is formed between the outer peripheral surface of the extended portion 82 of the main valve element 29 and the inner peripheral surface of the valve hole, in the control valve 101 according to the seventh embodiment, the cross-sectional area-fixed passage is formed by a slit 103 formed in a skirt 102 of the main valve element 29. More specifically, in the control valve 101, the main valve element 29 of the main valve 20 is integrally formed with the skirt 102 which is axially slidable in the valve hole, and the slit 103 is formed in the skirt 102, whereby a passage is formed the cross-sectional area which is not changeable with respect to the change in the stroke of the main valve element 29 along the axis thereof. The main valve element 29 illustrated in FIG. 12, by way of example, has one slit 103 formed in the hollow cylindrical skirt 102 extended downward from a tapered face via which the main valve element 29 is seated on the main valve seat 28, at a location downward of the seating position of the main valve element 29, as viewed in FIG. 12. Of course, there may be formed a plurality of slits 103 along the circumference of the skirt 102.

Since the skirt 102 integrally formed with the main valve element 29 of the main valve 20 is axially slidably fitted in the valve hole of the main valve 20, the main valve element 29 having the above-described shape is not wobbled and the passage cross-sectional area defined by the slit 103 is not changed even slightly even if lateral load is applied to the main valve element 29 by the flow of high-pressure refrigerant. Further, the main valve element 29 has a function of a bearing supporting the drive shaft 35 disposed in a manner extending therethrough, and hence is capable of holding the valve element 33 of the pilot valve 21 on the same axis as that of the valve seat 32 of the pilot valve 21.

Although the present invention is described in detail heretofore based on the preferred embodiments thereof, it is by no means limited to the specific forms thereof. For example, in the above-described first to sixth embodiments, the solenoid for control of the pilot valve 21 is disposed on a side of the main valve 20 opposite to a side thereof where the pilot valve 21 is disposed, this is not limitative, but of course the solenoid may be disposed on a side of the pilot valve 21 opposite to a side thereof where the main valve 20 is disposed.

The control valve for a variable displacement compressor, according to the present invention, is configured such that the solenoid does not control the main valve to change the passage cross-sectional area of a refrigerant passage, but sets the valve lift of the pilot valve having a smaller valve section than that of the main valve. This makes it possible to provide a stable flow rate control. Further, the main valve and the pilot valve are configured to operate in a manner interlocked with each other, which is advantageous in that the flow rate control can be realized by a very simple construction.

Further, in the variable displacement compressor, there occurs a large differential pressure between during operation and during stoppage of operation, and when the compressor is changed from an operating state into a non-operating state, pressure corresponding to the differential pressure is returned to the discharge chamber at a dash. To prevent this, a check valve has been conventionally disposed at an outlet port of the compressor. In the control valve according to the present invention, the main valve has a check valve structure in which it is lifted only depending on the flow rate of refrigerant flowing in one direction toward the outlet port. This is advantageous in that it is possible to dispense with the check valve disposed at the outlet port, and thereby reduce the cost of the compressor.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. A control valve for a variable displacement compressor, for providing control such that a flow rate of refrigerant discharged from the compressor becomes constant, comprising: a main valve that is disposed in a first refrigerant passage formed between a first port communicating with a discharge chamber of the compressor and a second port communicating with an outlet port of the compressor, such that the main valve is lifted in a valve-opening direction to set the first refrigerant passage to a cross-sectional area-fixed passage having a predetermined passage cross-sectional area in response to a flow of refrigerant from the first port to the second port, and closed when a flow rate of the flow of refrigerant is slight or zero; a pilot valve that is disposed into a second refrigerant passage formed between the first port and a third port communicating with a crankcase of the compressor, for controlling a flow rate of refrigerant flowing from the first port to the third port according to a differential pressure across the cross-sectional area-fixed passage; and a solenoid that sets the pilot valve to a predetermined valve lift by an external signal.
 2. The control valve according to claim 1, wherein the main valve and the pilot valve are lifted in a same lifting direction and arranged on a same axis, and the pilot valve senses the differential pressure generated across the cross-sectional area-fixed passage, based on a change in a flow rate of refrigerant flowing through the main valve, to thereby directly control a lift of the pilot valve.
 3. The control valve according to claim 2, wherein the solenoid is arranged on the same axis as the main valve and the pilot valve, and holds the pilot valve in a fully-open state when the solenoid is not energized.
 4. A control valve for a variable displacement compressor, for providing control such that a flow rate of refrigerant discharged from the compressor becomes constant, comprising: a main valve that has a main valve seat formed in a refrigerant passage communicating between a first port connected to a discharge chamber of the compressor and a second port connected to an outlet port of the compressor, and a main valve element that is disposed at a location downstream of the main valve seat, in a state urged in a valve-closing direction such that the main valve element is movable to and away from the main valve seat, and is lifted from the main valve seat in response to a flow of refrigerant from the first port to the second port, for setting the first refrigerant passage to a cross-sectional area-fixed passage having a predetermined passage cross-sectional area; a pilot valve that has a valve seat formed in a second refrigerant passage communicating between the first port and a third port connected to a crankcase of the compressor, and a valve element disposed at a location upstream of the valve seat in a state urged in a valve-opening direction such that the valve element is movable to and away from the valve seat, and at the same time operates in a manner interlocked with the main valve element when the main valve is set to the cross-sectional area-fixed passage, the pilot valve being arranged on a same axis as the main valve; and a solenoid disposed on a same axis as the main valve and the pilot valve, for setting the pilot valve to a predetermined valve lift by an external signal.
 5. The control valve according to claim 4, wherein the valve element of the pilot valve is formed integrally with a shaft extending through a through hole formed in the main valve element of the main valve, the shaft having a stopper member that stops the main valve element when the main valve element is lifted from the main valve seat in response to the flow of refrigerant from the first port to the second port, to thereby set the main valve to the cross-sectional area-fixed passage.
 6. The control valve according to claim 5, wherein the valve element of the pilot valve, the shaft, and a drive shaft of the solenoid are formed integrally with each other.
 7. The control valve according to claim 5, wherein the shaft has a protrusion that protrudes radially outward, and closes the through hole of the main valve element when the main valve is closed.
 8. The control valve according to claim 5, wherein the valve element of the pilot valve has a guide integrally formed therewith, the guide being formed by axially extending the valve element such that a periphery of the guide is in sliding contact with an inner wall of a valve hole of the pilot valve.
 9. The control valve according to claim 4, wherein the main valve element of the main valve has an extended portion that is always positioned within a valve hole of the main valve, and wherein the cross-sectional area-fixed passage which the main valve element is to set is defined between an outer peripheral surface of the extended portion and an inner peripheral surface of a valve hole of the main valve.
 10. The control valve according to claim 4, wherein the main valve element of the main valve has a skirt axially slidable in a valve hole of the main valve, the skirt being formed with a slit to thereby form the cross-sectional area-fixed passage which the main valve element is to set.
 11. The control valve according to claim 4, wherein the main valve element of the main valve defines the cross-sectional area-fixed passage which the main valve element is to set, between an outer peripheral surface thereof and an inner peripheral surface of a cylinder accommodating the main valve element.
 12. The control valve according to claim 4, wherein the pilot valve is a poppet valve disposed such that the poppet valve is movable to and away from the valve seat.
 13. The control valve according to claim 4, wherein the pilot valve is a slide valve having a valve hole into which the valve element can be inserted or from which the valve element can be removed. 